conodonts from the kechika formation and road river group...

Conodonts from the Kechika Formation and RoadRiver Group (Lower to Upper Ordovician) of theCassiar Terrane, northern British Columbia1

Leanne J. Pyle and Christopher R. Barnes

Abstract: This study examines the lower Paleozoic stratigraphy of the Cassiar Terrane from three key sections com-prising an east–west transect across the terrane. The Cassiar Terrane, west of the Northern Rocky Mountain Trench,consists of a Neoproterozoic to Triassic succession and is a fragment of the Cordilleran Miogeocline that has been dis-placed northward. The amount of displacement from its original position remains controversial. Conodonts from theCassiar Terrane have been previously reported from only a few reconnaissance studies. More than 3000 m of stratahave been measured and examined in detail and 85 conodont samples collected. A total of 926 identifiable conodontelements are assigned to 31 species representing 21 genera. The conodonts are mainly representative of theMidcontinent Faunal Realm, but some also represent the Atlantic Realm. Conodonts from the upper Kechika Formationand base of the Road River Group are Early Ordovician (Tremadocian) in age, and those from the upper Road RiverGroup range into the Upper Ordovician (Caradocian). The detailed Ordovician stratigraphy and temporal constraints es-tablished by conodont biostratigraphy provide for correlation to coeval facies of ancestral North America. The onset ofRoad River sedimentation in the mid-Tremadocian is, however, older than that in the Macdonald Platform to the east(early Arenigian). This onset timing may help link the Cassiar Terrane to a specific part of the miogeocline from whichit was transported.

Résumé: Cette étude examine la stratigraphie du Paléozoïque inférieur du terrane de Cassiar à partir de trois sectionsclefs comprenant un transect est-ouest à travers le terrane. Le terrane de Cassiar, à l’ouest du sillon septentrional desRocheuses, comprend une séquence du néo-Protérozoïque au Trias et représente un fragment du miogéocline de la Cor-dillère qui a été déplacé vers le nord. La distance de déplacement par rapport à sa position originale demeure contro-versée. Les Conodontes du terrane de Cassiar n’ont été signalés antérieurement que dans quelques études dereconnaissance. Des strates ont été mesurées et examinées en détail sur plus de 3000 m et 85 échantillons de Conodon-tes ont été recueillis. Neuf cent vingt-six (926) éléments identifiables de Conodontes ont été assignés à 31 espèces re-présentant 21 genres. Les Conodontes sont surtout représentatifs du domaine faunique du centre du continent, maisquelques-uns représentent aussi le domaine de l’Atlantique. Les Conodontes de la partie supérieure de la Formation deKechika et de la base du Groupe de Road River datent de l’Ordovicien précoce (Trémadocien) et ceux de la partie su-périeure du Groupe de Road River atteignent l’Ordovicien supérieur (Caradocien). La stratigraphie détaillée del’Ordovicien et les contraintes temporelles imposées par la biostratigraphie des Conodontes permettent une corrélation àdes faciès contemporains dans l’ancienne Amérique du Nord. La sédimentation du Road River au Trémadocien moyena toutefois débuté plus tard que dans la plate-forme de Macdonald vers l’est (Arénigien précoce). Ce moment du débutpeut aider à relier le terrane de Cassiar à une partie spécifique du miogéocline d’où il provient.

[Traduit par la Rédaction] 1401

Pyle and BarnesIntroduction

The parautochthonous Cassiar Terrane represents a segmentof the Cordilleran Miogeocline bounded to the east by theTintina – Northern Rocky Mountain Trench (NRMT) Fault,which offsets the miogeoclinal strata from those of ancestralNorth America (Fig. 1). The western boundary of the CassiarTerrane is the Intermontane Superterrane, which accreted to

North America in the Middle Jurassic (Gabrielse and Yorath1991). Geologic and paleomagnetic measurements indicatethe terrane was displaced northward along a dextral strike-slipfault system (Tintina – NRMT Fault) by a minimum of lessthan 500 km (Price and Carmichael 1986) or up to 900 km(Gabrielse 1985) from the Kakwa Platform (Fig. 1). Maximumestimates based on paleomagnetic data of the Slide MountainTerrane indicate movement over 2000 km (Richards et al.

Can. J. Earth Sci.38: 1387–1401 (2001) © 2001 NRC Canada

1387

DOI: 10.1139/cjes-38-10-1387

Received October 30, 2000. Accepted April 5, 2001. Published on the NRC Research Press Web site at http://cjes.nrc.ca onSeptember 28, 2001.

Paper handled by Associate Editor B. Chatterton.

L.J. Pyle2 and C.R. Barnes.School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6,Canada.

1Lithoprobe Contribution 1199.2Corresponding author (e-mail: [email protected]).

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1993) or, based on Cambrian stratigraphy, up to 1700 km asa margin segment from Idaho (Pope and Sears 1997; Fig. 2).

In the Cassiar Terrane, previous work on lower Paleozoicconodonts has been restricted to a few small Cambrian toDevonian collections made in the study area during regionalmapping projects. In this study, detailed sampling for conodontswas carried out across an east–west transect of the CassiarTerrane using three principal stratigraphic sections (Fig. 3).This study is part of a larger project directed at examiningthe lower Paleozoic stratigraphy and conodonts from UpperCambrian to Lower Silurian platform to basin facies of theNorthern Canadian Cordilleran Miogeocline (Pyle andBarnes 2000, 2001).

A total of 3032 m of strata was measured and described indetail, and 85 conodont samples were collected (4–5 kgeach) through the Kechika Formation and Road RiverGroup. The conodont samples were taken from carbonatebeds and processed through standard acid-dissolution tech-niques followed by concentration of conodont elements withheavy liquid (sodium polytungstate) and magnetic separation.The samples yielded 926 identifiable conodont elements,which have colour alteration index (CAI) values rangingfrom 3 to 5, indicating burial temperatures of 110–200°C to

over 300°C. The conodonts have been assigned to 31 speciesrepresenting 21 genera that are representative mainly of theMidcontinent Realm; however, species characteristic of theAtlantic Realm are also present.

Lithostratigraphy

The lower Paleozoic Kechika Formation and Road RiverGroup have been examined from three key sections: nearMoodie Creek; south of Deadwood Lake; and near the town-ship of Cassiar, at the base of Mount McDame (Fig. 3). Thestratigraphy of the Kechika Formation and Road RiverGroup is broadly similar to that of the miogeoclinal succes-sion east of the NRMT recently reported by Pyle and Barnes(2000).

Gabrielse (1963, 1979, 1998) described the miogeoclinalsuccession of the Cassiar Platform, originally referred to asthe Pelly–Cassiar Platform (Gabrielse 1967), duringregional-scale mapping within the McDame (National Topo-graphic System (NTS) 104 P) and Cry Lake (104 I) mapareas. Gabrielse (1963) was the first to describe the Kechika(as a group) at its type locality in the McDame map area.Kechika strata have been reported from the Cry Lake (104 I)and McDame (104 P) map areas west of the NRMT(Gabrielse 1962, 1963). Nelson and Bradford (1989, 1993)mapped part of the geology of the Cassiar Terrane.

In the type area, faunas reported include graptolites,trilobites, brachiopods, bryozoans, and cephalopods, whichprovide an approximate age from the Late Cambrian to earlyLate Ordovician (Gabrielse in Glass 1990). In the CassiarMountains, Norford (1962) described the overlying SilurianSandpile Group and its fauna.

The stratigraphy of the three sections, Moodie Creek,Deadwood Lake, and Cassiar – Mount McDame (Fig. 3), hasbeen described in detail by Pyle and Barnes (2000). Thecontact of the Kechika Formation with the overlying RoadRiver Group is conformable and gradational over less than1 m at both the Moodie Creek and Deadwood Lake sections(Figs. 4, 5).

At Moodie Creek, the Kechika Formation (1770 m, tec-tonically thickened) disconformably overlies the LowerCambrian Rosella Formation and consists of a variety oflithologies. The section is fault repeated such that the maxi-mum thickness in the area is approximately 900 m(Gabrielse 1998). Units are of low metamorphic grade likelydue to alkaline sills and dykes in close proximity, describedby Pell (1994). Units included pink-brown sericitic, cleavedphyllite, orange-brown massive dolostone with prominentquartz veins, green argillaceous, sheared siltstone and greyweathered, thin- to massive-bedded dolomitic limestone.Conodonts were recovered from the base of the overlyingRoad River Group, and only the uppermost Kechika Forma-tion is illustrated in Fig. 3. The Road River Group measuredfrom Moodie Creek (88 m) consists of cleaved grey andbrown shale and recrystallized silty limestone and dolostone.The overlying dolomitic siltstone and sandstone are assignedto the Sandpile Formation (late Llandovery to early Wenlock;Gabrielse 1998), and the contact appears to be conformableand gradational over a few metres.

At Deadwood Lake, calcareous Road River Group(427.5 m) conformably and gradationally overlies the light

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1388 Can. J. Earth Sci. Vol. 38, 2001

Fig. 1. Map showing lower Paleozoic paleogeography and presentposition of the Cassiar Terrane (modified from Cecile et al. 1997).

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Pyle and Barnes 1389

Fig. 2. Map of United States and Canadian Cordillera with Cassiar Platform translated (A) 600 km south in accordance with paleomagneticdata from Butler et al. (1988), and (B) to its proposed site of deposition in accordance with subsequent >2000 km northward translationof Slide Mountain Terrane (Richards et al. 1993; modified from Pope and Sears 1997).

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grey weathering shale and thin-bedded limestone of theKechika Formation (65.5 m). The Road River Group is di-vided into four informal units (Pyle and Barnes 2000;Fig. 5). The basal unit (155 m) consists of lenticular lime-stone and interbedded shale in metre-scale packages, whichweather orange-grey. The lenses increase in number andlateral continuity upsection. Unit 2 is a series of greyquartzite beds, quartz veins, interbedded dolostone, andblack phyllite (117 m). A third unit (52 m) consists oflargely grey, dolomitic siltstone, black shale and phyllite,and minor lime mudstone beds. Unit 4 (144 m) is beddedlime mudstone to grainstone interbedded with black shale,which decreases from 30–50% at the base to less than 5%at the top of the unit. Some beds are undulatory and con-tain chert nodules. Grainstone becomes abundant near thetop of the unit represented in part by phosphatic lags. Theunit is disconformably overlain by massive-bedded, lightgrey dolostone, which Gabrielse (1963) initially called theSandpile Group and now the Sandpile Formation(Gabrielse 1998).

The Road River Group examined in two creeks at theMount McDame section consists of 120–200 m of blue-black shale and slate interbedded with rare nodular limemudstone. Volcanics were observed near the top of the blackshale units, and the Road River Group is conformably over-

lain by sandstone of the Ramhorn Formation, as defined byGabrielse (1998). The conodont samples from this sectionwere barren.

Conodont biostratigraphy

Previously, no detailed biostratigraphic studies have beencarried out in the lower Paleozoic strata of the CassiarTerrane. Pohler and Orchard (1990) reported three speciesidentified from two small collections from the CassiarTerrane. The conodont fauna from the upper Kechika For-mation and Road River Group of the Moodie Creek andDeadwood Lake sections is assigned to 31 species representing21 genera (Tables 1, 2). Among these, several zonal speciesare present.

The biostratigraphy of the Kechika Formation and basalformation of the Road River Group, the Ospika Formation,has been established from nine stratigraphic sections east ofthe NRMT by Pyle and Barnes (2001; Figs. 3, 6). Based onthis framework, the conodonts recovered from the CassiarTerrane establish that the Kechika Formation – Road RiverGroup boundary lies within theRossodus manitouensisZone(middle Tremadocian).Rossodus manitouensisRepetski andEthington occurs within the uppermost Kechika Formationat the Deadwood Lake section (sample DL-96-2) and within

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Fig. 3. Map showing geographic localities of Cassiar Terrane sections in Cry Lake (NTS 104 P) and Kechika (NTS 94 L) map areas.Kechika River approximates the Northern Rocky Mountain Trench (NRMT). Cordilleran miogeoclinal section localities east of theNRMT are also shown (NTS map areas 94 F and 94 K).

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the base of the Road River Group at the Moodie Creek section(sample MC-95-A1; Figs. 4, 5). At the Deadwood Lake section,the zone is at least 84 m thick.

The fauna from the upper Kechika Formation and basalRoad River Group of the Cassiar Terrane (Figs. 4, 5)includesR. manitouensis, Cordylodus angulatusPander, andlonger ranging species ofCordylodus, such asC. lindstromiDruce and Jones andC. caseyiDruce and Jones,Utahconusutahensis Miller, Acanthodus lineatus Furnish,Drepanoistodus pervetusNowlan, and VariabiloconusbassleriFurnish. New species (formally named by Pyle andBarnes 2001) of Midcontinent Realm affinity that are presentat this interval in the Cassiar Terrane and east of the NRMTare Drepanoistodus minutus, Cordylodus delicatus, andStriatodontus strigatus. These data indicate that the KechikaFormation – Road River Group contact is significantly olderthan that observed east of the NRMT, where the base of theRoad River Group is within thePrioniodus elegansZone,early Arenigian.

The Road River Group at the Deadwood Lake sectionranges into theParoistodus proteusZone (late Tremadocian),the base of which occurs at the level of the first appearanceof Paroistodus proteus(Lindström), as was originally proposedby Lindström (1971). The thickness of the zone was notdetermined, asP. proteusoccurs only in sample DL-96-13,168 m above the base of the Road River Group.

The conodont fauna also indicates that the Road RiverGroup ranges into the middle Caradocian, Upper Ordovician(Amorphognathus superbusZone), at the Deadwood Lakesection (59°01′N, 128°23′W), southwest end of Deadwood

Lake, Cry Lake map area (Figs. 3, 6). The base of theA. superbusZone is defined as the level of the first appearanceof Amorphognathus superbusRhodes (Bergström 1971).The base of the zone is 417.5 m above the base of the mea-sured section and 352 m above the base of the Road RiverGroup (sample DL-96-21). The top and thickness of thezone are not constrained, and it is cut by a disconformity.The zone was originally defined in Baltoscandia byBergström (1971), who divided it into subzones and dis-cussed its widespread occurrence in Europe and NorthAmerica and use for intercontinental correlation. Characteristicspecies that occur in the zone from this study includeDrepanoistodus basiovalis(Sergeeva),Ansella jemtlandica(Löfgren), Yaoxianognathussp., and the long-ranging speciesPhragmodus undatusBranson and Mehl.

Graptolites collected from the top of the Road RiverGroup (sample DL-96-26) comprise an assemblage of threediplograptid taxa, which indicate thelinearis Zone and a lateCaradocian – early Ashgillian age (H. Williams, personalcommunication, 2000). Macrofossils from the top of theRoad River Group at Deadwood Lake were interpreted byG.W. Sinclair (in Gabrielse 1963, pp. 38–39) as Middle orLate Ordovician (Trentonian or Edenian = Caradocian) age,which is in agreement with the conodont and graptolite ages.

Discussion

There is considerable debate about the original position ofthe Cassiar Terrane along the Cordilleran Miogeocline. Aproblem in the reconciliation of paleomagnetic and geologic

Fig. 4. Biozonation and stratigraphic distribution of conodont species from the upper part of the Moodie Creek section (58°46′N,127°33′W; section located 1 km east of Moodie Creek, 7 km south-southeast of Moodie Lakes; 6 km of ridge trending southwest–northeast, then north; section strongly deformed, possible stratigraphic repetition or omission due to faulting in the lower part). Gp.,Group; Fm., Formation; Mb., Member.

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data lies in the large-displacement evidence suggested bypaleomagnetic measurements within the Cassiar Terrane andthe structures responsible for the movement. Dextral motionalong the Tintina – NRMT Fault system from the mid-Cretaceous (105 Ma) to early Tertiary ranges from 450 to900 km. The terrane may have originated a minimum of

450 km south of its present position during the early Paleozoic,on line with the Kakwa Platform (Gabrielse 1985; Price andCarmichael 1986; Cecile and Norford 1993; Fig. 1).

Paleomagnetic data from PermianParafusulina-bearinglimestone of the Sylvester Allochthon, which overlies themiogeoclinal succession of the Cassiar Terrane and was

Fig. 5. Biozonation and stratigraphic distribution of conodont species from the Deadwood Lake section (59°01′N, 128°23′W; located atthe southwest end of Deadwood Lake, in creek bed which drains into the southernmost tip of the lake). Abbreviations as in Fig. 4.

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likely accreted by the Middle Jurassic (Gabrielse and Yorath1991), indicate 700 km northward translation of the CassiarTerrane since 105 Ma (Butler et al. 1988). In contrast, Richardset al. (1993) interpreted other paleomagnetic data to suggestthat part of the Sylvester Allochthon has been translatednorthward over 2000 km relative to North America betweenthe Early Permian and Jurassic. The movement may have

occurred before its emplacement onto the Cassiar Terrane. Popeand Sears (1997) proposed that the terrane originated about1700 km south of its present position, based on Cambrianstra-tigraphy and archeocyathid faunas, which restores theCassiar Terrane to fill a miogeoclinal gap in Idaho (Fig. 2).The main problem in establishing these large displacementestimates is that the dextral faults to accommodate the trans-

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KechikaFormation Road River Group

Distance above base (m): 13 28 97 181 388.5 417.5 427.5 437.5 457.5 467.5 478.5 485.5 494

Sample No. (DL-96-): 2 3 7 13 18 21 22 23 25 26 27 28 29 TotalAcanthodus lineatus 4 9 168 181Amorphognathus superbus 63 63Ansella jemtlandica 1 1Colaptoconussp. 7 18 25Cordylodus angulatus 18 18Cordylodus caseyi 2 2Cordylodus delicatus 2 2Cordylodus lindstromi 3 6 9Drepanoistodus basiovalis 4 3 1 2 2 3 15Drepanoistodus pervetus 10 36 46Drepanoistodus minutus 3 2 5Drepanoistoduscf. D. n.sp. A 8 8Macerodus dianae? 2 2Macerodussp.? 1 12 13Panderodus sulcatus 1 1 7 9Paroistodus proteus 7 7Periodonsp.? 3 3Phragmodus undatus 9 29 48 86Plectodina tenuis 13 13Protopanderodus liripipus 5 5Pseudooneotodus mitratus 4 4Ramiform indet. 1 1Rossodus manitouensis 52 164 216Striatodontus prolificus 3 3Tricostatuscf. T. infundibulum 2 2 4Utahconus utahensis 5 5Variabilioconus bassleri 48 48Yaoxianognathussp. 4 4Total 4 92 483 15 7 67 3 3 2 12 10 29 71 798

Table 1. Number of conodont elements recovered from Deadwood Lake section, uppermost Kechika Formation and Road River Group.

Distance above base (m): 1 13 40

Sample No.: MC-95-A1 MC-95-A3 MC-95-A5 TotalAcanthodus lineatus 19 19Acanthodus uncinatus 7 7Colaptoconussp. 5 1 6Cordylodus angulatus 3 3Cordylodus lindstromi 2 2Drepanoistodus minutus 6 6Drepanoistodus pervetus 14 1 15Rossodus manitouensis 20 20Striatodontus strigatus 2 15 17Utahconus utahensis 11 11Variabiloconus bassleri 22 22Total 111 2 15 128

Table 2. Number of conodont elements recovered from the Moodie Creek section, Road River Group.

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Fig. 6. Biostratigraphic correlation chart for the Ordovician system. Conodont and graptolite zones after Goldman and Bergström(1997), Fortey et al. (1995), Harris et al. (1995), and Webby (1995), and time scale after Webby (1998) and Cooper and Nowlan(1999). Abbreviated subzones:R. musk., Rossodus muskwaensis; R. sheff., Rossodus sheffieldensis; G. con., Graciloconus concinnus;C. bol., Colaptoconus bolites; T. sw., Tropodus sweeti; B. ex., Bergstroemognathus extensus; J. va., Juanognathus variabilis. Abbreviatedstages and substages: Strefford’n, Streffordian; Pus., Pusgillian; Caut, Cautleyan; Rawth, Rawtheyan; Hirnan., Hirnantian; Croix.,Croixian; Tremp., Trempealeauan; Black., Blackhillsian; Rang., Rangerian; Maysvill., Maysvillian; Richmond., Richmondian; Gamach.,Gamachian.%CT, data from Cassiar Terrane; N. Am., North American.

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lation have not been identified, that is, those west of theNRMT Fault between the Intermontane Superterrane andancestral North America and the southern continuation ofthe NRMT.

An important aspect in estimating displacements alongfault systems is the offset of geologic units. This study, onthe basis of the Ordovician stratigraphic succession, confirmsthat the Kechika Formation and Road River Group arebroadly similar to the lithologies of the miogeoclinal successionobserved east of the NRMT in northern British Columbia(Macdonald Platform) and may have originally been continuouswith the Kakwa Platform to the south (Cecile and Norford1993). The lack of Ordovician miogeoclinal strata inboard inIdaho makes a lithological match to that part of themiogeocline difficult.

The conodont fauna is largely of Midcontinent Realmaffinity but does contain some Atlantic Realm species. Theage of the Kechika Formation – Road River Group boundaryas established by conodonts suggests an older age (mid-Tremadocian) within the Cassiar succession compared withthat east of the NRMT (lower Arenigian).

Although the paleomagnetic data that require large postmid-Cretaceous transport of the terrane are in conflict, thedetailed stratigraphy and age constraints on the Ordoviciansuccession are a contribution to the Cassiar Terrane puzzle.Future work to establish a section of the autochthonousmiogeocline that has a similar age range for the onset ofRoad River Group sedimentation may help establish the initialposition of the Cassiar Terrane.

Taxonomic remarks

The following taxa require no further taxonomic descriptionor only brief taxonomic remarks. The suprageneric classifi-cation of orders of conodonts proposed in Sweet (1988) andmodified by Aldridge and Smith (1993) is followed herein.Additional suprageneric ranks of Craniata Linnaeus,Vertebrata Linnaeus, and Gnathostomata Cope have beendetermined through cladistic analysis by Donoghue et al.(2000). All illustrated specimens are deposited in the Na-tional Type Repository in the Geological Survey of Canada(GSC). Several new species that are described in detail inPyle and Barnes (2001) are present in the Road River Groupof the Cassiar Terrane and are included with a brief remark.

Phylum Chordata Bateson, 1886Class Conodonta Pander, 1856Genus ColaptoconusKennedy, 1994Colaptoconussp.

(Pl. 1, figs. 15, 16)

RemarksLimited material is assigned toColaptoconusbased on the

extreme rounded lateral costae and concave posterior cuspface that bears a strong, rounded posterior carina. The sym-metrical c element has a rounded, shallow basal cavity andbase, which is expanded anteroposteriorly. Anterior cuspface is rounded with a weak carina from tip to base.

OccurrenceRossodus manitouensisZone, Kechika Formation and

Road River Group.

MaterialThirty-one elements.

RepositoryGSC 119654, GSC 119655.

Genus CordylodusPander 1856Cordylodus delicatus(Pyle and Barnes 2001)

(Pl. 1, fig. 5)

RemarksA few specimens of the small, delicate species of

Cordylodus with extremely wide angle between slender,elongate cusp and first denticle of posterior denticulated processare present in this collection.Cordylodus delicatusis similarto C. primitivus in its primitive characters, such as a deepbasal cavity and simple morphology.

OccurrenceRossodus manitouensisZone, Road River Group.

MaterialTwo elements.

RepositoryGSC 119644.

Genus DrepanoistodusLindström 1971Drepanoistodus minutus(Pyle and Barnes 2001)

(Pl. 1, fig. 10)

RemarksThe small, delicate apparatus is distinguished from other

species of Drepanoistodus by comprising simple,unornamented coniforms characterized by small size andsmall base with slender, extremely elongate cusp. The c elementbears an erect, long, laterally compressed cusp with sharplyrounded anterior and posterior cusp margins. Its base issmall and flared equally both posteriorly and anteriorly, andthe basal margin is sinuous, arching under anterobasal corner.


Road River Group.

MaterialEleven elements.


Drepanoistoduscf. Drepanoistodusn.sp. A (Pyle andBarnes 2001)

(Pl. 2, figs. 2–5)

RemarksElements which are similar to those ofDrepanoistodus

n.sp. A (Pyle and Barnes 2001) occur within the DeadwoodLake section. The a elements are distinct, in which the sharpanterior margin is more developed into a keel that deflects

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from the posterior cusp margin to join the base in ananterolateral position. Other a elements do not have such astrong development of anterolateral keel and the base hastwo carinae, near each basal corner. Base on these elementsopens anteriorly. The e element is different fromDrepanoistodusn.sp. A in being nongeniculate with recurvedcusp. Base has inner lateral flare and is not as expanded pos-teriorly.

OccurrenceParoistodus proteusZone, Road River Group.

MaterialSix a elements, two e elements.

RepositoryGSC 119667 – GSC 119670.

Genus MacerodusFåhræus and Nowlan, 1978Macerodus dianaeFåhræus and Nowlan, 1978?

(Pl. 1, fig. 25)

RemarksTwo specimens are questionably assigned toM. dianae

based on the long, compressed cusp with quadrate cross section.However, the compression is uneven and is strongest at theanterobasal corner.

OccurrenceParoistodus proteusZone, Road River Group.

MaterialTwo elements.


Macerodussp.?(Pl. 1, figs. 17–21)

RemarksElements of two morphotypes (a and e) have elongate,

compressed cusps and long, broad, posteriorly extendedbases. The a elements have laterally compressed, recurvedcusps with sharply rounded anterior and posterior cusp margins.Cusp is slender, about two-thirds width of base, andunornamented. Base is expanded posteriorly. Anterobasalcorner is straight in some elements (Pl. 1, fig. 19) as anteriorcusp margin meets base at right angle. In other elements, theanterobasal corner is rounded. Basal margin is flat; basaloutline oval.

The e element is compressed with long, recurved cusp.Cusp has sharp margins and is unornamented. Base is shortand anterobasal corner is rounded and compressed. Baseflares open posteriorly and has rounded basal outline.

DiscussionThe specimens are tentatively assigned toMacerodus, but

more material is need to ascertain the relationship. The eelement is unlike that in other species ofMacerodus, but thea elements bear some similarity toMacerodusn.sp. B? ofPyle and Barnes (2001).


MaterialThirteen elements.

RepositoryGSC 119656 – GSC 119660.

GenusPseudooneotodusDrygant, 1974Pseudooneotodus mitratus(Moskalenko, 1973)

(Pl. 2, fig. 13)

RemarksNowlan and Barnes (1981) described the simple conical

elements as having a deep basal cavity and folded lateralfaces. They also showed symmetry differences among elements.The few elements recovered from the Road River Groupconform to their description.

© 2001 NRC Canada


Plate 1. All specimens are from the Deadwood Lake section except the specimen in fig. 14, which is from the Moodie Creek section.All views are lateral except where noted.figs. 1, 2. Rossodus manitouensisRepetski and Ethington 1983. (1) a element, posterolateralview, DL-96-7, GSC 119640, ×70. (2) e element, DL-96-7, GSC 119641, ×70.figs. 3, 4.Cordylodus angulatusPander 1856. (3) a element,DL-96-7, GSC 119642, ×70. (4) e element, DL-96-7, GSC 119643, ×70.fig. 5. Cordylodus delicatusPyle and Barnes 2001, a element,DL-96-7, GSC 119644, ×90.fig. 6. Cordylodus caseyiDruce and Jones 1971, a element, DL-96-7, GSC 119645, ×125.fig. 7.Cordylodus lindstromiDruce and Jones 1971, a element, DL-96-3, GSC 119646, ×75.figs. 8, 9. Acanthodus lineatus(Furnish 1938).(8) a element, DL-96-7, GSC 119647, ×85. (9) e element, DL-96-7, GSC 119648, ×85.fig. 10. Drepanoistodus minutusPyle andBarnes 2001, c element, DL-96-7, GSC 119649, ×130.fig. 11. Drepanoistodus pervetusNowlan 1985, a element, DL-96-3, GSC119650, ×85.figs. 12, 13.Tricostatuscf. T. infundibulumPyle and Barnes 2001. (12) c element, posterior view, DL-96-3, GSC119651, ×78. (13) a element, posterolateral view, DL-96-7, GSC 119652, ×105.fig. 14. Striatodontus strigatusPyle and Barnes 2001,a element, MC-95-A1, GSC 119653, ×43.figs. 15, 16.Colaptoconussp. c elements, posterior views, DL-96-3, GSC 119654, GSC119655, ×125.figs. 17–21.Macerodussp.? (17) e element, DL-96-7, GSC 119656, ×80. (18–21) a elements, DL-96-7, GSC 119657 – GSC119660, ×80.fig. 22. Utahconus utahensis(Miller 1969). e element, DL-96-3, GSC 119661, ×145.figs. 23, 24.Variabiloconus bassleri(Furnish 1938). (23) a element, DL-96-7, GSC 119662, ×90. (24) e element, DL-96-7, GSC 119663, ×90.fig. 25. Macerodus dianaeFåhræus and Nowlan 1978? a element, DL-96-13, GSC 119664, ×80.fig. 26. Striatodontus prolificusJi and Barnes 1994, a element,DL-96-7, GSC 119665, ×120.

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OccurrencePhragmodus undatusZone, Road River Group, Cassiar

Terrane.

MaterialFour elements.


Genus RossodusRepetski and Ethington, 1983Rossodus manitouensisRepetski and Ethington, 1983

(Pl. 1, figs. 1, 2)

RemarksThe apparatus ofR. manitouensiswas described adequately

by Ji and Barnes (1994) as containing four morphotypes (a,b, c, and e). In the Cassiar collection, two additionalnongeniculate compressed elements are recognized, whichhave a broad, laterally compressed, and flexed cusp.


Road River Group.

MaterialTwo hundred and thirty-six elements.

RepositoryGSC 119640 and GSC 119641.

Genus StriatodontusJi and Barnes, 1994Striatodontus strigatus(Pyle and Barnes 2001)

(Pl. 1, fig. 14)

RemarksThe elements are similar in the overall morphology to

Striatodontus prolificusJi and Barnes, but are more robustand have more prominent striae covering the elements anddeeper longitudinal grooves. They have been assigned to anew species based on the apparatus of at least threemorphotypes (a, b, and c elements) of robust but slendercones with slightly expanded bases and cusps, which arecovered by fine striae and bear two prominent longitudinalgrooves on inner lateral or posterior cusp face.


MaterialSeventeen elements.


Genus TricostatusJi and Barnes, 1994Tricostatuscf. T. infundibulum(Pyle and Barnes 2001)

(Pl. 1, figs. 12, 13)

RemarksA few samples from the Deadwood Lake section yield

specimens that are similar toT. infundibulum, a short-ranging species in the mid-Tremadocian Kechika Formationeast of the NRMT (Rossodus manitouensisZone), describedby Pyle and Barnes (2001). Elements have the invertedfunnel-shaped costae on the posterior cusp face, but the baseis not as triangular nor as wide as that inT. infundibulum.




Genus UtahconusMiller, 1980Utahconus utahensis(Miller 1980)

(Pl. 1, fig. 22)

RemarksThe apparatus ofU utahensis has previously been

described as bimembrate by Miller (1980), who illustratedunicostate (a) and bicostate (e) elements. Pyle and Barnes(2001) reconstruct a multielement apparatus, which includessix element morphotypes (a, b, c, and three types of e elements)and observed an abundance of compressed e elements in theapparatus, perhaps suggesting there were more pairs of thethree types of e elements. The smallest e morphotype isdiagnostic and present within the Cassiar collection (Pl. 1,fig. 22). Utahconusis the direct ancestor ofRossodus.

© 2001 NRC Canada


Plate 2. All specimens are from the Deadwood Lake section. All views are lateral except where noted.fig. 1. Paroistodus proteus(Lindström 1955). S element, DL-96-13, GSC 119666, ×55.figs. 2–5.Drepanoistoduscf. D. n.sp. A. Pyle and Barnes 2001. (2) e ele-ment, DL-96-13, GSC 119667, ×53. (3–5) a elements, DL-96-13, GSC 119668 – GSC 119670, ×53.figs. 6, 7. Protopanderodusliripipus Kennedy, Barnes and Uyeno 1979. (6) c element, DL-96-26, GSC 119671, ×63. (7) a–b element, DL-96-26, GSC 119672,×63. fig. 8. Periodonsp.? S element, DL-96-18, GSC 119673, ×80.fig. 9. Ramiform indet. posterior view, DL-96-23, GSC 119674,×150. figs. 10–12.Yaoxianognathussp. (10) Sc element, DL-96-21, GSC 119677, ×80. (11, 12) P element, DL-96-21, GSC 119675,×65. fig. 13. Pseudooneotodus mitratus(Moskalenko 1973), oral view, DL-96-26, GSC 119676, ×70.figs. 14, 15.AmorphognathussuperbusRhodes 1953. (14, 15) Pa elements, oral views, DL-96-21, GSC 119678, GSC 119679, ×53.figs. 16–20.PhragmodusundatusBranson and Mehl 1933. (16) Pb element, DL-96-29, GSC 119679, ×125. (17) Sc element, DL-96-29, GSC 119680, ×70. (18)Sa element, DL-96-29, GSC 119681, ×90. (19) Pa element, DL-96-29, GSC 119682, ×90. (20) M element, DL-96-29, GSC 119683,×90. fig. 21. Panderodus sulcatus(Fåhræus 1966). DL-96-29, GSC 119684, ×80.figs. 22–25.Plectodina tenuis(Branson and Mehl1933). (22) M element, lateral views, DL-96-29, GSC 119685, ×80. (23, 24) S elements, lateral views, DL-96-29, GSC 119686, GSC119687, ×80. (25) P element, lateral view, DL-96-29, GSC 119689, ×80.

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Road River Group.

MaterialSixteen elements.


Genus YaoxianognathusAn in An et al. 1985Yaoxianognathussp.

(Pl. 2, figs. 10–12)

RemarksOnly fragmentary specimens have been recovered from

the Road River Group, Cassiar Terrane. The P elements areextremely thin and are most similar toY. ani (Zhen et al.1999) in being unarched with a straight lower margin. However,as elements are broken, it is difficult to determine theprominence of the cusp, number of denticles, and length ofanterior process, which are diagnostic characters.

OccurrenceAmorphognathus superbusZone, Road River Group,

Cassiar Terrane.



Ramiform indet.(Pl. 2, fig. 9)

DescriptionOne broken specimen from the Deadwood Lake section is

symmetrical ramiform element which has slender, laterallycompressed cusp with keeled lateral cusp margins and keeledposterior cusp margin. Two lateral processes are compressedand denticulate.

OccurrenceAmorphognathus superbusZone, Road River Group.

MaterialOne element.


Acknowledgments

We gratefully acknowledge primary financial support forthe project provided by Lithoprobe Slave – Northern CordilleraLithospheric Evolution (SNORCLE) Project and the NaturalSciences and Engineering Research Council of Canada andadditional support from the Northern Scientific ResearchTraining Program and a Geological Society of Americagrant. Logistical support for fieldwork was provided by the

British Columbia Geological Survey, and discussions onfield localities with Hu Gabrielse, JoAnne Nelson, and BrianNorford were appreciated. We thank Henry Williams forgraptolite identifications and the reviewers of the manuscript,S.M. Bergström and H. Gabrielse, for their time and helpfulsuggestions. We also thank Corwin Sullivan and DiannePellerin for cheerful and able field assistance and MichelleLandry, Marjorie Deagle, and Emily Delahaye for laboratoryassistance and preparation of figures.

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conodonts from the kechika formation and road river group...

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